Method of fabricating vertical structure LEDs

ABSTRACT

A method of fabricating semiconductor devices, such as GaN LEDs, on insulating substrates, such as sapphire. Semiconductor layers are produced on the insulating substrate using normal semiconductor processing techniques. Trenches that define the boundaries of the individual devices are then formed through the semiconductor layers and into the insulating substrate, beneficially by using inductive coupled plasma reactive ion etching. The trenches are then filled with an easily removed layer. A metal support structure is then formed on the semiconductor layers (such as by plating or by deposition) and the insulating substrate is removed. Electrical contacts, a passivation layer, and metallic pads are then added to the individual devices, and the individual devices are then diced out.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to semiconductor device fabrication. Moreparticularly, the present invention relates to a method of fabricatingvertical devices using a metal support layer.

2. Discussion of the Related Art

Light emitting diodes (“LEDs”) are well-known semiconductor devices thatconvert electrical current into light. The color (wavelength) of thelight that is emitted by an LED depends on the semiconductor materialthat is used to fabricate the LED. This is because the wavelength of theemitted light depends on the semiconductor material's band-gap, whichrepresents the energy difference between the material's valence band andconduction band electrons.

Gallium-Nitride (GaN) has gained much attention from LED researchers.One reason for this is that GaN can be combined with indium to produceInGaN/GaN semiconductor layers that emit green, blue, and white light.This wavelength control ability enables an LED semiconductor designer totailor material characteristics to achieve beneficial devicecharacteristics. For example, GaN enables an LED semiconductor designerto produce blue LEDs, which are beneficial in optical recordings, andwhite LEDs, which can replace incandescent lamps.

Because of the foregoing and other advantageous, the market forGaN-based LEDs is rapidly growing. Accordingly, GaN-basedopto-electronic device technology has rapidly evolved since theircommercial introduction in 1994. Because the efficiency of GaN lightemitting diodes has surpassed that of incandescent lighting, and is nowcomparable with that of fluorescent lighting, the market for GaN basedLEDs is expected to continue its rapid growth.

Despite the rapid development of GaN device technology, GaN devices aretoo expensive for many applications. One reason for this is the highcost of manufacturing GaN-based devices, which in turn is related to thedifficulties of growing GaN epitaxial layers and of subsequently dicingout completed GaN-based devices.

GaN-based devices are typically fabricated on sapphire substrates. Thisis because sapphire wafers are commercially available in dimensions thatare suitable for mass-producing GaN-based devices, because sapphiresupports relatively high-quality GaN epitaxial layer growths, andbecause of the extensive temperature handling capability of sapphire.

Typically, GaN-based devices are fabricated on 2″ diameter sapphirewafers that are either 330 or 430 microns thick. Such a diameter enablesthe fabrication of thousands of individual devices, while the thicknessis sufficient to support device fabrication without excessive waferwarping. Furthermore, sapphire is chemically and thermally stable, has ahigh melting temperature that enables high temperature fabricationprocesses, has a high bonding energy (122.4 Kcal/mole), and a highdielectric constant. Chemically, sapphires are crystalline aluminumoxide, Al₂O₃.

Fabricating semiconductor devices on sapphire is typically performed bygrowing an n-GaN epitaxial layer on a sapphire substrate using metaloxide chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE).Then, a plurality of individual devices, such as GaN LEDs, is fabricatedon the epitaxial layer using normal semiconductor processing techniques.After the individual devices are fabricated they must be diced out(separated) of the sapphire substrate. However, since sapphires areextremely hard, are chemically resistant, and do not have natural cleaveangles, sapphire substrates are difficult to dice. Indeed, dicingtypically requires that the sapphire substrate be thinned to about 100microns by mechanical grinding, lapping, and/or polishing. It should benoted that such mechanical steps are time consuming and expensive, andthat such steps reduce device yields. Even after thinning sapphiresremain difficult to dice. Thus, after thinning and polishing, thesapphire substrate is usually attached to a supporting tape. Then, adiamond saw or stylus forms scribe lines between the individual devices.Such scribing typically requires at least half an hour to process onesubstrate, adding even more to the manufacturing costs. Additionally,since the scribe lines have to be relatively wide to enable subsequentdicing the device yields are reduced, adding even more to manufacturingcosts. After scribing, the sapphire substrates can be rolled using arubber roller or struck with a knife-edge to produce stress cracks thatcan be used to dice out the individual semiconductor devices. Suchmechanical handling reduces yields even more.

Of note, because sapphire is an insulator the LED device topologies thatare available when using sapphire substrates (or other insulatingsubstrates) are, in practice, limited to lateral and verticaltopologies. In the lateral topology the metallic electrical contactsthat are used to inject electrical current into the LED are both locatedon upper surfaces (or on the same side of the substrate). In thevertical topology one metallic contact is on an upper surface, thesapphire (insulating) substrate is removed, and the other contact islocated on a lower surface.

FIGS. 1A and 1B illustrate a typical lateral GaN-based LED 20 that isfabricated on a sapphire substrate 22. Referring now specifically toFIG. 1A, an n-GaN buffer layer 24 is formed on the substrate 22. Arelatively thick n-GaN layer 26 is formed on the buffer layer 24. Anactive layer 28 having multiple quantum wells ofaluminum-indium-gallium-nitride (AlInGaN) or of InGaN/GaN is then formedon the n-type GaN layer 26. A p-GaN layer 30 is then formed on theactive layer 26. A transparent conductive layer 32 is then formed on thep-GaN layer 30. The transparent conductive layer 32 may be made of anysuitable material, such as Ru/Au, Ni/Au or indium-tin-oxide (ITO). Ap-type electrode 34 is then formed on one side of the transparentconductive layer 32. Suitable p-type electrode materials include Ni/Au,Pd/Au, Pd/Ni and Pt. A pad 36 is then formed on the p-type electrode 34.Beneficially, the pad 36 is Au. The transparent conductive layer 32, thep-GaN layer 30, the active layer 28 and part of the n-GaN layer 26 areetched to form a step. Because of the difficulty of wet etching GaN, adry etch is usual used. This etching requires additional lithography andstripping processes. Furthermore, plasma damage to the GaN step surfaceis often sustained during the dry-etch process. The LED 20 is completedby forming an n-electrode pad 38 (usually Au) and a pad 40 on the step.

FIG. 1B illustrates a top down view of the LED 20. As can be seen,lateral GaN-based LEDs have a significant draw back in that having bothmetal contacts (36 and 40) on the same side of the LED significantlyreduces the surface area available for light emission. As shown in FIG.1B the metal contacts 36 and 40 are physically close together.Furthermore, as previously mentioned the pads 36 are often Au. Whenexternal wire bonds are attached to the pads 36 and 40, the Au oftenspreads. Au spreading can bring the electrical contacts even closertogether. Such closely spaced electrodes 34 are highly susceptible toESD damage.

FIGS. 2A and 2B illustrate a vertical GaN-based LED 50 that was formedon a sapphire substrate that was subsequently removed. Referring nowspecifically to FIG. 2A, the LED 50 includes a GaN buffer layer 54having an n-metal contact 56 on a bottom side, and a relatively thickn-GaN layer 58 on the other. The n-metal contact 56 is beneficiallyformed from a high reflectively layer that is overlaid by a highconductivity metal, including, for example, Au. An active layer 60having multiple quantum wells is formed on the n-type GaN layer 58, anda p-GaN layer 62 is formed on the active layer 60. A transparentconductive layer 64 is then formed on the p-GaN layer 62, and a p-typeelectrode 66 is formed on the transparent conductive layer 64. A pad 68is formed on the p-type electrode 66. The materials for the variouslayers are similar to those used in the lateral LED 20. The verticalGaN-based LED 50 as the advantage that etching a step is not required.However, to locate the n-metal contact 56 below the GaN buffer layer 54the sapphire substrate (not shown) has to be removed. Such removal canbe difficult, particularly if device yields are of concern. However, asdiscussed subsequently, sapphire substrate removal using laser lift offis known.

Referring now to FIG. 2B, vertical GaN-based LEDs have the advantagethat only one metal contact (68) blocks light. Thus, to provide the sameamount of light emission area, lateral GaN-based LEDs must have a largersurface area, which lowers device yields. Furthermore, the reflectinglayer of the n-type contact 56 of vertical GaN-based LEDs reflect lightthat is otherwise absorbed in lateral GaN-based LEDs. Thus, to emit thesame amount of light as a vertical GaN-based LED, a lateral GaN-basedLED must have a significantly larger surface area. Because of theseissues, a 2″ diameter sapphire wafer can produce about 35,000 verticalGaN-based LEDs, but only about 12,000 lateral GaN-based LEDs.Furthermore, the lateral topology is more vulnerable to staticelectricity, primarily because the two electrodes (36 and 40) are soclose together. Additionally, as the lateral topology is fabricated onan insulating substrate, and as the vertical topology can be attached toa heat sink, the lateral topology has relatively poor thermaldissipation. Thus, in many respects the vertical topology isoperationally superior to the lateral topology.

However, most GaN-based LEDs fabricated with a lateral topology. This isprimarily because of the difficulties of removing the insulatingsubstrate and of handling the GaN wafer structure without a supportingsubstrate. Despite these problems, removal of an insulation (growth)substrate and subsequent wafer bonding of the resulting GaN-based waferon a Si substrate using Pd/In metal layers has been demonstrated forvery small area wafers, approx. 1 cm by 1 cm. But, substrate removal andsubsequent wafer bonding of large area wafers remains very difficult dueto inhomogeneous bonding between the GaN wafer and the 2^(nd)(substitutional) substrate. This is mainly due to wafer bowing duringand after laser lift off.

Thus, it is apparent that a new method of fabricating vertical topologydevices would be beneficial. In particular, a method that provides formechanical stability of semiconductor wafer layers, that enablesvertical topology electrical contact formation, and that improves heatdissipation would be highly useful, particularly with devices subject tohigh electrical currents, such as laser diodes or high-power LEDs.Beneficially, such a method would enable forming multiple semiconductorlayers on an insulating substrate, the adding of a top support metallayer that provides for top electrical contacts and for structuralstability, and the removal of the insulating substrate. Of particularbenefit would be a new method of forming partially fabricatedsemiconductor devices on a sapphire (or other insulating) substrate, theadding of a top support metal layer over the partially fabricatedsemiconductor layers, the removal of the sapphire (or other insulating)substrate, the formation of bottom electrical contacts, and the dicingof the top support metal layer to yield a plurality of devices.Specifically advantageous would be fabrication process that producesvertical topology GaN-based LEDs.

SUMMARY OF THE INVENTION

The following summary of the invention is provided to facilitate anunderstanding of some of the innovative features unique to the presentinvention, and is not intended to be a full description. A fullappreciation of the various aspects of the invention can be gained bytalking the entire specification, claims, drawings, and abstract as awhole.

The principles of the present invention provide for a method offabricating semiconductor devices on insulating substrates by firstforming semiconductor layers on the insulating substrate, followed byforming a metal layer over the semiconductor layers, followed by removalof the insulating substrate to isolate a structurally supported wafercomprised of the formed semiconductor layers and the metal layer. Themetal layer supports the semiconductor layers to prevent warping and/orother damage and provides for electrical contacts. Beneficially, themetal layer includes a metal, such as Cu, Cr, Ni, Au, Ag, Mo, Pt, Pd, W,or Al, or a metal containing material such as titanium nitride. Formingof the metal layer can be performed in numerous ways, for example, byelectroplating, by electro-less plating, by CVD, or by sputtering.Subsequently, bottom electrical contacts can be added to thesemiconductor layers and then individual semiconductor devices can bediced from the resulting structure.

The principles of the present invention further provide for a method offabricating vertical topology GaN-based devices on an insulatingsubstrate by the use of a metal support film and by the subsequentremoval of the insulating substrate. According to that method,semiconductor layers for the GaN-based devices are formed on aninsulating (sapphire) substrate using normal semiconductor fabricationtechniques. Then, trenches that define the boundaries of the individualdevices are formed through the semiconductor layers. Those trenches mayalso be formed into the insulating substrate. Trench forming isbeneficially performed using inductive coupled plasma reactive ionetching (ICPRIE). The trenches are then filled with an easily removedlayer (such as a photo-resist). A metal support structure is then formedon the semiconductor layers. Beneficially, the metal support structureincludes a metal, such as Cu, Cr, Ni, Au, Ag, Mo, Pt, Pd, W, or Al, or ametal-containing material such as titanium nitride. Forming of the metalsupport structure can be performed in numerous ways, for example, byelectroplating, by electro-less plating, by CVD, or by sputtering. Theinsulating substrate is then removed, beneficially using a laser-liftoff process. Electrical contacts, a passivation layer, and metallic padsare then added to the individual devices, and the individual devices arethen diced out.

The principles of the present invention specifically provide for amethod of fabricating vertical topology GaN-based LEDs on sapphiresubstrates. According to that method, semiconductor layers for thevertical topology GaN-based LEDs are formed on a sapphire substrateusing normal semiconductor fabrication techniques. Then, trenches thatdefine the boundaries of the individual vertical topology GaN-based LEDsare formed through the semiconductor layers. Those trenches may also beformed into the sapphire substrate. Trench forming is beneficiallyperformed using inductive coupled plasma reactive ion etching (ICPRIE).Beneficially, the trenches are fabricated using ICPRIE. The trenches arethen beneficially filled with an easily removed layer (such as aphoto-resist). A metal support structure is then formed on thesemiconductor layers. Beneficially, the metal support structure includesa metal, such as Cu, Cr, Ni, Au, Ag, Mo, Pt Pd, W, or Al, or ametal-containing material such as titanium nitride. Forming of the metallayer can be performed in numerous ways, for example, by electroplating,by electro-less plating, by CVD, or by sputtering. The sapphiresubstrate is then removed, beneficially using a laser-lift off process.Electrical contacts, a passivation layer, and metallic pads are thenadded to the individual LEDs, and the individual LEDs are then dicedout.

The novel features of the present invention will become apparent tothose of skill in the art upon examination of the following detaileddescription of the invention or can be learned by practice of thepresent invention. It should be understood, however, that the detaileddescription of the invention and the specific examples presented, whileindicating certain embodiments of the present invention, are providedfor illustration purposes only because various changes and modificationswithin the spirit and scope of the invention will become apparent tothose of skill in the art from the detailed description of the inventionand claims that follow.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying figures, in which like reference numerals refer toidentical or functionally-similar elements throughout the separate viewsand which are incorporated in and form part of the specification,further illustrate the present invention and, together with the detaileddescription of the invention, serve to explain the principles of thepresent invention.

In the drawings:

FIG. 1A illustrates a sectional view of a typical lateral topologyGaN-based LED;

FIG. 1B shows a top down view of the GaN-based LED illustrated in FIG.1A;

FIG. 2A illustrates a sectional view of a typical vertical topologyGaN-based LED;

FIG. 2B shows a top down view of the GaN-based LED illustrated in FIG.2A; and

FIGS. 3-15 illustrate steps of forming a light emitting diode that arein accord with the principles of the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The principles of the present invention provide for methods offabricating semiconductor devices, such as GaN-based vertical topologyLEDs, on insulating substrates, such as sapphire substrates, using metalsupport films. While those principles are illustrated in a detaileddescription of a method of fabricating vertical topology GaN-based LEDson a sapphire substrate, those principles are broader than thatillustrated method. Therefore, the principles of the present inventionare to be limited only by the appended claims as understood underUnited. States Patent Laws.

FIGS. 3-15 illustrate a method of manufacturing vertical topologyGaN-based light emitting diodes (LEDs) on sapphire substrates. Sapphiresubstrates are readily available in suitable sizes, are thermally,chemically, and mechanically stable, are relatively inexpensive, andsupport the growth of good quality GaN epitaxial layers. It should beunderstood that those figures are not to scale.

Referring now to FIG. 3, initially a GaN-based LED layer structure isformed on a 330-430 micron-thick, 2″ diameter (0001) sapphire substrate122. The GaN-based LED layer structure includes an n-GaN buffer layer124, an InGaN/GaN active layer 126 (beneficially having the propercomposition to emit blue light) on the buffer layer 124, and a p-GaNcontact layer 128 on the active layer 126.

Still referring to FIG. 3, the buffer layer 124 beneficially includesboth a 2 μm undoped GaN layer formed directly on the substrate, and a 1μm thick, n-type, silicon doped, GaN layer. The p-GaN contact layer 128is beneficially about 0.05 μm thick and is doped with Mg. Overall, theGaN-based LED layer structure is beneficially less than about 5 micronsthick. Various standard epitaxial growth techniques, such as vapor phaseepitaxy, MOCVD, and MBE, together with suitable dopants and othermaterials, can be used to produce the GaN-based LED layer structure.

Referring now to FIG. 4, trenches 130 are formed through the verticaltopology GaN-based LED layer structure. Those trenches 130 may extendinto the sapphire substrate 122. The trenches 130 define the individualLED semiconductor structures that will be produced. Each individual LEDsemiconductor structure is beneficially a square about 200 microns wide.The trenches 130 are beneficially narrower than about 10 microns(preferably close to 1 micron) and extend deeper than about 5 micronsinto the sapphire substrate 122. The trenches 130 assist a subsequentchip separation process.

Because of the hardness of sapphire and GaN, the trenches 130 arebeneficially formed in the structure of FIG. 3 using reactive ionetching, preferably inductively coupled plasma reactive ion etching (ICPRIE). Forming trenches using ICP RIE has two main steps: forming scribelines and etching. Scribe lines are formed on the structure of FIG. 3using a photo-resist pattern in which areas of the sapphire substrate122 where the trenches 130 are to be formed are exposed. The exposedareas are the scribe lines, while all other areas are covered byphoto-resist. The photo-resist pattern is beneficially fabricated from arelatively hard photo-resist material that withstands intense plasma.For example, the photo-resist could be AZ 9260, while the developer usedto develop the photo-resist to form the scribe lines could be AZ MIF500.

In the illustrated example, the photo-resist is beneficially spin coatedto a thickness of about 10 microns. However, in general, thephoto-resist thickness should be about the same as the thickness of thevertical topology GaN-based LED layer structure plus the etch depth intothe sapphire substrate 122. This helps ensure that the photo-resist maskremains intact during etching. Because it is difficult to form a thickphoto-resist coating in one step, the photo-resist can be applied in twocoats, each about 5 microns thick. The first photo-resist coat is spincoated on and then soft baked, for example, at 90° F. for about 15minutes. Then, the second photo-resist coat is applied in a similarmanner, but is soft baked, for example, at 110° F. for about 8 minutes.The photo-resist coating is then patterned to form the scribe lines.This is beneficially performed using lithographic techniques anddevelopment. Development takes a relatively long time because of thethickness of the photo-resist coating. After development, thephoto-resist pattern is hard baked, for example, at about 80° F. forabout 30 minutes. Then, the hard baked photo-resist is beneficiallydipped in a MCB (Metal Chlorobenzene) treatment for about 3.5 minutes.Such dipping further hardens the photo-resist.

After the scribe lines are defined, the structure of FIG. 3 is etched.Referring now to FIG. 5, the ICP RIE etch process is performed byplacing the structure of FIG. 3 on a bottom electrode 132 in a RIEchamber 134 having an insulating window 136 (beneficially a 1 cm-thickquartz window). The bottom electrode 132 is connected to a bias voltagesupply 138 that biases the structure of FIG. 3 to enable etching. Thebias voltage supply 138 beneficially supplies 13.56 MHz RF power and aDC-bias voltage. The distance from the insulating window 136 to thebottom electrode 132 is beneficially about 6.5 cm. A gas mixture of Cl₂and BCl₃, and possibly Ar, is injected into the RIE chamber 134 througha reactive gas port 140. Furthermore, electrons are injected into thechamber via a port 142. A 2.5-turn or so spiral Cu coil 144 is locatedabove the insulating window 136. Radio frequency (RF) power at 13.56 MHzis applied to the coil 144 from an RF source 146. It should be notedthat magnetic fields are produced at right angles to the insulatingwindow 136 by the RF power.

Still referring to FIG. 5, electrons present in the electromagneticfield produced by the coil 144 collide with neutral particles of theinjected gases, resulting in the formation of ions and neutrals, whichproduce plasma. Ions in the plasma are accelerated toward the structureof FIG. 3 by the bias voltage applied by the bias voltage supply 138 tothe bottom electrode 132. The accelerated ions pass through the scribelines, forming the etch channels 130 (see FIG. 4).

Referring now to FIG. 6, after the trenches 130 are formed, thinp-contacts 150 are formed on the individual LED semiconductor structuresof the GaN-based LED layer structure. Those contacts 150 arebeneficially comprised of Pt/Au, Pd/Au, Ru/Au, Ni/Au, Cr/Au, or ofindium tin oxide (ITO)/Au and are less then 10 nm. Such contacts can beformed using a vacuum evaporator (electron beam, thermal, sputter),followed by thermal annealing at an intermediate temperature(approximately 300-700° C.).

As shown in FIG. 7, after the contacts 150 are formed, the trenches 130are filled with an easily removed material (beneficially a photo-resist)to form posts 154.

Referring now to FIG. 8, after the posts 154 are formed, a metal supportlayer 156 approximately 50 μm is formed over the posts 154 and over thep-contacts 150. The posts 154 prevent the metal that forms the metalsupport layer 156 from entering into the trenches. The metal supportlayer 156 is beneficially comprised of a metal having good electricaland thermal conductivity and that is easily formed, such as byelectroplating, by electro-less plating, by CVD, or by sputtering.Before electroplating or electro-less plating, it is beneficial to coatthe surface with a suitable metal, such as by sputtering. For example,the metal support layer 156 can be Cu, Cr, Ni, Au, Ag, Mo, Pt, Pd, W, orAl. Alternatively, the metal support layer 156 can be comprised of ametal-containing material such as titanium nitride.

Turning now to FIG. 9, the sapphire substrate 122 is then removed fromthe remainder of the structure using light 158 from an eximer layer(having a wavelength less than 350 nanometers), while the sapphiresubstrate is biased away from the remainder of the structure (such as byuse of vacuum chucks). The laser beam 158 passes through the sapphiresubstrate 122, causing localized heating at the junction of the sapphiresubstrate 122 and the n-GaN buffer layer 124. That heat decomposes theGaN at the interface of the sapphire substrate, which, together with thebias, causes the sapphire substrate 122 to separate, reference FIG. 10.It is beneficial to hold the other side of the structure with a vacuumchuck during laser lift off. This enable easy application of aseparation bias.

Laser lift off processes are described in U.S. Pat. No. 6,071,795 toCheung et al., entitled, “Separation of Thin Films From TransparentSubstrates By Selective Optical Processing,” issued on Jun. 6, 2000, andin Kelly et al. “Optical process for liftoff of group III-nitridefilms”, Physica Status Solidi (a) vol. 159, 1997, pp. R3-R4.Beneficially, the metal support layer 156 fully supports the individualLED semiconductor structures during and after separation of the sapphiresubstrate.

Still referring to FIG. 10, the posts 154 are then removed, leaving thetrenches 130 behind.

Turning now to FIG. 11, the structure of FIG. 10 is inverted.

Then, the side opposite the metal support layer 156 is cleaned with HClto remove Ga droplets (laser beam 158 heating separates GaN into Ga+N).After cleaning, ICP RIE polishing (using Cl₂ an/or Cl₂+BCl₃) isperformed to smooth the exposed surface (which is rough due to theseparation of the sapphire substrate). Polishing produces an atomicallyflat surface of pure n-GaN on the n-GaN buffer layer 124.

Turning now to FIG. 12, n-type ohmic contacts 160 are formed on then-GaN buffer layer 124 using normal semiconductor-processing techniques.Beneficially, the n-type ohmic contacts 160 are comprised ofTi/Al-related materials.

Turning now to FIG. 13, to protect the semiconductor layers fromsubsequent processing, a passivation layer 162 is formed on the n-typeohmic contacts 160 and in the trenches 130. Electrical insulationcomprised of SiO₂ or Si₃N₄ are suitable passivation layer materials.Additionally, as shown, the passivation layer 162 is patterned to exposetop surface portions of the n-type ohmic contacts 160.

Turning now to FIG. 14, after the passivation layer 162 is formed, metalpads 164 are formed on the n-type ohmic contacts 160. As shown in FIG.14, the metal pads 164 extend over portions of the passivation layer162. The metal pads 164 are beneficially comprised of Cr and Au.

After the metal pads 164 are formed, individual devices can be dicedout. Referring now to FIG. 15, dicing is beneficially accomplished usingphotolithographic techniques to etch through the metal support layer 156to the bottom of the passivation layer 162 (at the bottom of thetrenches 130) and by removal of the passivation layer 162.Alternatively, sawing can be used. In practice, it is probably better toperform sawing at less than about 0° C. The result is a plurality ofvertical topology GaN LEDs 199 on conductive substrates.

The foregoing has described forming trenches 130 before laser lift offof the sapphire substrate 122. However, this is not required. Thesapphire substrate 122 could be removed first, and then trenches 130 canbe formed.

The embodiments and examples set forth herein are presented to bestexplain the present invention and its practical application and tothereby enable those skilled in the art to make and utilize theinvention. Those skilled in the art, however, will recognize that theforegoing description and examples have been presented for the purposeof illustration and example only. Other variations and modifications ofthe present invention will be apparent to those of skill in the art, andit is the intent of the appended claims that such variations andmodifications be covered. The description as set forth is not intendedto be exhaustive or to limit the scope of the invention. Manymodifications and variations are possible in light of the above teachingwithout departing from the spirit and scope of the following claims. Itis contemplated that the use of the present invention can involvecomponents having different characteristics. It is intended that thescope of the present invention be defined by the claims appended hereto,giving full cognizance to equivalents in all respects.

1-42. (canceled)
 43. A vertical light emitting device, comprising: asupport layer; a semiconductor layer comprising a first GaN-based layer,a second GaN-based layer, and an active layer located between the firstand second GaN-based layer; a first electrode located at one side of thesemiconductor layer; a coating on the first electrode that facilitatesthe support layer to grow on the coating; and a second electrode locatedat an opposite side of the semiconductor layer such that the secondelectrode is vertically aligned with the first electrode and current canflow between the first electrode and the second electrode.
 44. Thevertical light emitting device according to claim 43, further comprisingan at least one of a passivation layer over the exposed portions of thesemiconductor layer.
 45. The vertical light emitting device according toclaim 44, wherein the passivation layer comprises a material includingat least one of Si, O and N.
 46. The vertical light emitting deviceaccording to claim 43, further comprising the support layer, wherein thesupport layer includes a metal selected from a group including Cu, Cr,Ni, Au, Ag, Mo, Pt, Pd, W, Ti and Al.
 47. The vertical light emittingdevice according to claim 43, wherein the first GaN-based layer is ap-GaN layer and the second GaN-based layer is an n-GaN layer.
 48. Thevertical light emitting device according to claim 44, further comprisingan undoped GaN layer over the second GaN-based layer.
 49. The verticallight emitting device according to claim 43, wherein the passivationlayer is disposed higher than the second electrode.
 50. The verticallight emitting device according to claim 43, wherein the coatingincludes a metal.
 51. The vertical light emitting device according toclaim 43, wherein the support layer is grown using at least one ofelectroplating, electro-less plating, chemical vapor deposition, andsputtering.
 52. A vertical light emitting device, comprising: a supportlayer; a first GaN-based layer over the support layer; a first electrodedisposed between the support layer and the first GaN-based layer suchthat the first GaN-based layer is disposed over the first electrode; acoating on the first electrode; a second GaN-based layer thicker thanthe first GaN-based layer over the first GaN-based layer; a lightemitting layer disposed between the first GaN-based layer and the secondGaN-based layer; and a second electrode over the second GaN-based layer,wherein the first electrode is vertically aligned with the secondelectrode.
 53. The vertical light emitting device according to claim 52,further comprising at least one of a passivation layer over exposedportions of the first GaN-based layer, of the light emitting layers, andof the second GaN-based layer.
 54. The vertical light emitting deviceaccording to claim 53 wherein the passivation layer comprises materialincluding at least one of Si, O and N.
 55. The vertical light emittingdevice according to claim 52, wherein the support layer includes a metalselected from a group including Cu, Cr, Ni, Au, Ag, Mo, Pt, Pd, W, Tiand Al.
 56. The vertical light emitting device according to claim 52,wherein the first GaN-based layer is a p-GaN layer and the secondGaN-based layer is an n-GaN layer.
 57. The vertical light emittingdevice according to claim 56, further comprising an undoped GaN layerover the second GaN-based layer.
 58. The vertical light emitting deviceaccording to claim 53, wherein the passivation layer is disposed higherthan the second electrode.
 59. The vertical light emitting deviceaccording to claim 53, wherein the passivation layer is surrounding atleast two side portions of first GaN-based layer, of the light emittinglayer, and of the second GaN-based layer.
 60. The vertical lightemitting device according to claim 52, further comprising a passivationlayer disposed partially between the support layer and the firstGaN-based layer.
 61. The vertical light emitting device according toclaim 52, wherein the coating includes a metal.
 62. The vertical lightemitting device according to claim 52, wherein the coating on the firstelectrode facilitates the support layer to grow on the coating, andsupport layer is grown using at least one of electroplating,electro-less plating, chemical vapor deposition, and sputtering.